The present invention relates to vaporization and pressurization of liquid in a capillary pump, and relates particularly to mechanisms for optimizing fluid flow and pressure for vaporizing liquid traveling through multiple layers of a capillary pump.
Many applications utilize the gaseous form of a liquid. Vaporization devices have been designed to vaporize liquids and release the resulting vapor under pressure. In general, liquid that is supplied to the vaporization device becomes vaporized as it flows through the various device components. In applications in which a pressurized vapor stream is desired, prior devices usually require that liquid be supplied to the device under pressure or that the vapor be otherwise pressurized by external means. For example, in order to sustain the inflow of liquid in a pressurized boiler system, the liquid is usually supplied under at least as much pressure as that of the outgoing vapor. However, such pressurized liquid sources are usually inconvenient to use, heavy to transport, explosive, and prone to leakage through added valves. Often it is desirable to provide liquid from a non-pressurized liquid source.
Fluid flow in these vaporization devices may occur in various pathways of the device, such as through pores or channels extending through device components. Some current vaporization devices that use non-pressurized liquid supplies, utilize capillary flow to draw the liquid. Although flow by capillary action is relatively simple, it presents some difficult problems in optimizing vapor production and release.
In order create favorable conditions for vapor production, the flow of fluids through the vaporization device should be maximized. In general, a higher flow rate permits more liquid to be vaporized per unit of time. However, at the same time it is also important for vapor pressure to increase within the device so that the vapor may be released with a certain amount of force. For example, in combustion applications, vapor emitted under pressure allows for mixing of the vapor with air or oxygenated gas so that the vaporized fuel/gas mixture may be burned. Vapor that is released under high pressure has a high Reynolds number, resulting in turbulence and therefore more rapid mixing. Consequently, a hotter and cleaner-burning flame may be produced when the mixed vapor is ignited. In efforts to create sufficient pressure to make a clean-burning flame, many prior devices have been designed to be large and bulky. These cumbersome devices are often overly costly and are inconvenient for varied applications.
Thus, it is important for a capillary pump to have both high fluid flow and produce high pressure in a simple and compact device. The maximum flow rate, i.e. the most liquid flow capacity for a device per unit time, and pressure are often related. Where the maximum flow rate within a device is low, this is often due to a correlated pressure drop within the device. For example, viscous drag within the capillary structures of many vaporization devices leads to a reduction in maximum flow rate as well as a drop in pressure. Moreover, the problem of reduced fluid flow is accentuated in devices that. include small capillary pores. Although small pores may increase the capillary pressure, the viscous drag increases to a larger extent, resulting in less flow of liquid. Thus, these prior devices have limited flow capacity of vapor and liquid.
In addition, some vaporization devices attempt to address other vaporization issues at the compromise of flow rate and pressure. For instance, it is essential that supply liquid be protected from heat exposure in the device. Where the supply liquid becomes heated, vaporization may occur in the supply, which is accompanied by uncontrolled pressurization of the supply liquid. The resulting vaporization may be a safety hazard. In response, some prior devices use a very thick capillary component that serves multiple functions for the device, such as insulating the supply liquid, as well as providing capillary action and a controlled place for travelling liquid to become heated. However, this increased thickness of the capillary component creates a longer distance through which the fluid must flow and be subject to viscous drag within the capillaries. Thus, this thick component needlessly reduces the rate in which fluid travels through the device.
One way of controlling the rate of vaporization is by adjusting the heat supplied to the device. At times, an electrically powered heater may supply the energy to vaporize the fuel and the electrical power input may be varied. These heaters are usually intricate and expensive. It is advantageous to incorporate simple heating mechanisms within the device.
The optimization of vaporization of the device is further effected by varied heat distribution within a horizontal cross-sectional area of the device in the pathway for fluid flow. Where the device has a point that is lower in temperature than another point along a horizontal plane, the rate of vaporization at that point is also lower, thereby decreasing the effective cross-sectional area of the evaporating surface and increasing total viscous drag in the device. Thus, it is desirable to maintain even horizontal heat distribution within the device.
In general, the shortcomings of the current vaporization devices encompass thick multi-purpose components, which decrease the maximum fluid flow and pressurization of the devices. Furthermore, previous vaporization devices are often bulky, expensive and inconvenient for varied applications.
A capillary pump is provided for producing pressurized vapor emissions, which has layers that have varying properties and characteristics to serve different functions in creating optimal conditions to accomplish a high maximum fluid flow rate and pressurization. The layers create fluid pathways for heat and liquid/vapor to flow in opposing directions. One such layer is a vaporization layer sufficiently thin and encompassing an adequate area to reduce viscous drag of flowing liquid and vapor. The vaporization layer has small-sized pores to produce the capillary pressure necessary to draw the liquid through the layers of the device, as well as to support the pressurization of the resulting vapor. An ejection layer is also included having one or more openings to permit release of pressurized vapor. This ejection layer has an integrated heat transfer portion that has a plurality of pores or channels for conveying heat and providing a low fluidic drag area. A coating at least partially surrounds the outer surfaces of the pump to allow vapor pressure to increase.
In some embodiments, the pump additionally has a porous insulation layer to shield the liquid in the supply area from heat that may migrate through the thin vaporization layer. Furthermore, the capillary pump may include a porous preheat layer to raise the temperature of the liquid prior to the liquid entering the vaporization layer. In still further embodiments, a heat distribution layer may be included with smaller pores than the pores or channels of the heat transfer portion.
The ejection layer may have various configurations to assist in pump optimization. In one embodiment, the heat transfer region of the ejection layer may be formed by the space between multiple protruding posts. Furthermore, at least one of the opening(s) in the ejection layer may be a variable opening, such as a flexible plate with at least one slot or having a moveable plate that may at least partially uncover the opening. In further embodiments, the ejection layer may create the heat that is used in the vaporization region to create vapor. For example, the ejection layer may be integrated with a thick film electrical heater or comprise an electrically conductive material, or comprise a chemically reactive substance, e.g. lithium bromide, to create heat upon contact with an added substance, e.g. an aqueous solution, such as water.
The pump may be adapted for a variety of applications that require pressurized vapor. For combustion applications, the pump may incorporate or be associated with an energy converter to generate a flame from the released pressurized vapor. Such energy converter may include, for example, spark electrodes, glow wires, flint assemblies, or the like.